Priority to German Patent Application No. 100 60 826.4, which is hereby incorporated by reference herein, is hereby claimed.
The present invention relates to a spring element for fixing in place printing forms on printing form cylinders which are contained in printing units of rotary printing presses, the printing forms being printing forms which have a plate-shaped configuration and feature angularly bent leading edges and trailing edges.
European Patent No. 0 534 579 B2 relates to a device for changing printing plates in a rotary printing press. In this design approach, provision is made for a plurality of leaf springs which are each formed of a leaf spring member and have a U-shaped cross-section. These leaf springs are accommodated in a spring groove. The leaf springs each include a leg via which the leading end of the printing plate is retained in the clamping channel; the leaf springs, moreover, include a second leg via which an angularly bent trailing printing plate edge is fixed in place in the clamping channel of the printing form cylinder. A tensioning spindle is acted upon by a preloading element so that the tensioning spindle can be moved is such a manner that the leaf springs can act both upon a leading edge and upon a trailing edge of a printing plate.
The leaf spring arrangement known from European Patent EP 0 534 579 B2 involves the disadvantageous circumstance that, due to the narrow installation space, the leaf springs cannot be fitted into a preassembled tensioning shaft which is already integrated into the printing form cylinder.
In view of the indicated related art, an object of the present invention is to provide a spring element which is easy to mount and dismount, for fixing in place printing forms on cylinders.
According to the present invention, this objective may be achieved by a device or fixing printing forms on printing form cylinders of rotary printing presses, the printing forms extending into a clamping channel with their leading edges and trailing edges and, via clamping elements in the clamping channel, being tensioned on the lateral surface of the printing form cylinder in a circumferential direction of the printing form cylinder and retained in the clamping channel. The clamping elements are accommodated on a tensioning shaft which is rotatably accommodated in a bore of the printing form cylinder, and the clamping elements are designed as Y-shaped spring elements including a first and a second resilient section.
The advantages which can be attained using this design approach are to be seen above all in that a tension spring element configured in this manner needs an extremely small installation space and that it can be installed after the tensioning spindle has already been introduced into the receiving bore in the printing form cylinder accommodating the printing form. This involves that the installation work is made easier and rationalized; moreover, the spring element configured according to the present invention for fixing in place printing forms can be replaced in the clamping channel of a printing form cylinder easily. During the replacement of the clamping elements configured according to the present invention, it is not required to remove the cylinder from the side walls of the printing unit, which would result in unjustifiably long standstill times (downtime) of the respective printing unit. A further advantageous aspect of the design approach according to the present invention is to be seen in that a spring element having the design proposed according to the present invention allows both the printing form to be tensioned in a circumferential direction on the lateral surface of the respective printing form cylinder and the leading printing form edge to be fixed in place on a side wall of the clamping channel concurrently with the tensioning of the trailing printing form edge. The configuration of a spring element according to the present invention makes it possible for the printing form ends to be fixed in place in the clamping channel, involving a high retention force, while at the same time permitting compensating movements of the printing form on the lateral surface due to the flexural elasticity of the clamping element configured according to the present invention.
In an advantageous refinement of the idea of the present invention, a plurality of spring elements can be accommodated side by side in the clamping channel of the respective printing form cylinder. This permits an easy mounting or dismounting of the spring elements on printing units of rotary printing presses which contain extremely slender and therefore relatively wide printing form cylinders.
A first variant of an embodiment of the spring elements configured according to the present invention includes a first and a second resilient section made of flexurally elastic material of different material thickness. In this context, in a particularly simple manner in terms of production engineering, the first and the second resilient section can be made of materials of different material thickness which are joined to form a spring element configured according to the present invention, the spring qualities of the spring element being adjustable through the selection of the material thickness. Thus, for instance, the first resilient section which tensions the trailing edge of a printing form in a circumferential direction on the lateral surface of a printing cylinder can be designed with a higher, a greater material thickness in comparison with the second resilient section of the spring element projecting from the first resilient section in a Y-shaped manner.
To improve the transfer of the retention force, the first resilient section designed with a greater material thickness is provided with an angularly bent, hook-shaped end region via which the trailing edge of the printing form to be fixed in place on the lateral surface of the printing form cylinder is grasped and tensioned in a circumferential direction. Because of the flexural elasticity inherent in the first resilient section, the tensional force is permanently transferred to the printing form when the spring element is in a tensioning position.
At a spreading location, the second resilient section of the spring element branches off from the first resilient section in a Y-shaped fashion in a manner which reduces the required installation space. Because of this, the spring element configured according to the present invention can be inserted into the clamping channel provided on the printing form cylinder with the locating section ahead which can easily be introduced into the receiving slot of the tensioning shaft which accommodates and actuates the spring element.
The second resilient section projecting from the first resilient section in a Y-shaped manner includes a curved region at whose side facing the leading edge of the printing form, a linear contact region is formed. Via the linear contact region, the second section abuts against the leading edge of the printing form retained on a side wall of the printing form cylinder and fixes the leading edge permanently in place in the clamping channel while, at the same time, the first resilient section grips under the trailing edge of the printing form with its hook-shaped end, tensioning the printing form in a circumferential direction on the lateral surface of the printing form cylinder.
In addition to configuring the second resilient section of the spring element in a manner that a linear contact with the leading printing form edge is provided, this section can also be provided with coatings which increase the coefficient of friction, pin-shaped retaining elements extending through the angularly bent leading printing form edge, thus fixing in place the leading edge on a side wall of the clamping channel in the printing form cylinder.
In a further variant of an embodiment of the spring element configured according to the present invention, the spring element can be designed in one piece with a continuous locating section from which first and second resilient sections project in a Y-shaped manner. In this variant of an embodiment of the spring element proposed according to the present invention, the first and second resilient sections can be alternately formed on a workpiece in a segment-like manner. The first and second resilient sections are separated from each other by slot-shaped openings so that the one-piece spring element is easy to manufacture in terms of production engineering, using simple forming processes. In this context, according to the second variant of the design approach of the present invention, the end of the first resilient section of the spring element designed in one piece which end grasps the trailing edge of the printing form can be provided with a rounded region which reduces the risk of injury to the person who manually changes the printing form. Besides, the spring elements configured according to the present invention can, of course, also be used for retaining, tensioning and fixing in place plate-shaped printing forms which can be conveyed to the printing form cylinders of rotary printing presses or removed therefrom via automatic or semi-automatic printing plate changing devices.
The design approach proposed according to the present invention, can preferably be used on rotary printing presses, it being particularly preferred for use in web-fed rotary printing presses, for example short-run or newspaper presses.